The effects of commonly prescribed psychotropic drugs such as methylphenidate, and dextroamphetamine on the behavior of children from about 5 to 12 years of age who display short attention spans, hyperactivity, impulsivity, and are diagnosed as MBD (minimal brain dysfunction) will be systematically studied. A number of measures will be used to assess drug effects: teacher, parent, and physician rating scales; observer monitoring and video taping of classroom behavior; laboratory tests of attention focusing on the child's ability to allocate his attention to aspects of a stimulus; short-term memory tasks; psychological tests such as intelligence tests and impulsivity tests; growth in height, weight, and body composition; gas chromatographic and mass spectrometry analysis of metabolites in the blood and urine; and psychophysiological monitoring of attention. An anterospective long-term follow-up will be continued with about 120 children who received stimulant medication (some for 7 years), on children whose medication has been discontinued, and on cohort children. Studies of dose-response relationships between mg/kg doses of psychoactive drugs and learning performance, arithmetic, and social behavior in classrooms will be conducted.